Nucleic acids as fog stabilizers for photographic emulsions



United States Patent 3,512,982 NUCLEIC ACIDS AS FOG STABILIZERS FORPHOTOGRAPHIC EMULSIONS Robert C. Taber, William H. Russell, and CharlesA. Golie, Rochester, N.Y., assignors to Eastman Kodak Company,Rochester, N.Y., a corporation of New Jersey No Drawing. Filed Apr. 6,1967, Ser. No. 628,830 Int. Cl. G03c 5/30, 1/34 US. Cl. 96-665 12 ClaimsABSTRACT OF THE DISCLOSURE A photographic silver halide emulsion orphotographic element containing a fog-stabilizing amount of a nucleicacid, e.g., ribonucleic acid or deoxyribonucleic acid. Developingphotographic elements in the presence of a nucleic acid is alsodescribed.

BACKGROUND OF THE INVENTION Field of the invention This inventionrelates to new and improved antifoggants and stabilizers forphotographic elements and to photographic silver halide emulsionscontaining said antifoggants and stabilizers therein. The invention alsorelates to a process of developing photographic elements in the presenceof new and improved antifoggants.

Description of the prior art During development of a silver halideemulsion, small amounts of silver halide are reduced to metallic silverre gardless of whether or not they have been exposed. This reduction ofsilver ion produces a background fog which is more specifically referredto as chemical fog. This fog is particularly noticeable when the film isgiven more development than intended either because of longer processingtime or higher processing temperature or a combination of both.

Chemical fog, apparent in most silver halide systems, has been reducedby prior art methods of processing exposed silver halide amaterial inthe presence of compounds which restrict development of unexposed silverhalide. Such compounds can be incorporated in the silver halide emulsionor in the processing solutions for developing such silver halideemulsions. Compounds which have been found to have a chemical foginhibiting effect on emulsions which have been subjected to hightemperature and high humidity conditions are referred to as emulsionstabilizers. On the other hand, compounds which have been found to havechemical fog inhibiting effects on emulsions which have not been exposedto adverse storage conditions are referred to as antifoggants. Althougha large number of emulsion stabilizers and antifoggants have been usedin the prior art, many of these compounds cause undesirable losses inemulsion speed and contrast and others lack adequate compatibility withemulsion gelatin. Some addenda which have been used in the past tocontrol extended development fog have the disadvantage of attacking thelatent image. For example, mercuric chloride added to a photographicemulsion controls fog but results in loss of density if the exposed filmis not processed soon after exposure.

SUMMARY OF THE INVENTION According to one embodiment of this invention,there is incorporated into the silver halide emulsion of a photographicelement or in a layer contiguous to the silver halide emulsion, afog-stabilizing amount of a nucleic acid. The nucleic acid stabilizesthe emulsion against fog when Patented May 19, 1970 ice DESCRIPTION OFTHE PREFERRED EMBODIMENTS The nucleic acid may be incorporated into thesilver halide emulsion of a photographic element or in a layercontiguous to the silver halide emulsion in any amount which willstabilize the silver halide emulsion against fog. In general, aconcentration of the nucleic acid in an amount of from about 0.025 toabout 10, preferably about 0.050 to about 2, grams per mole of silver inthe silver halide emulsion can be used with good results.

Nucleic acids are made up of three components, liberated on acidhydrolysis: an organic base or bases, phosphoric acid and a sugar. Asfar as is known, the sugar unit is either ribose or 2-deoxyribose. Bothdeoxyribonucleic acid (DNA) and ribonucleic acid (RNA) contain the basesadenine, guanine and cytosine. In DNA, the fourth base is thymine whilein RNA the fourth base is uracil. In our invention, either DNA alone,RNA alone or mixtures of DNA and RNA can be employed.

The preparation of photographic silver halide emulsions such as aresuitably stabilized with a nucleic acid typically involves threeseparate operations: (1) emulsification and digestion of silver halide,(2) the freeing of the emulsion of excess Water-soluble salts, suitablyby washing with water, and (3) the second digestion or after-ripening toobtain increased emulsion speed or sensitivity. (Mees, The Theory of thePhotographic Process, 1954.) The nucleic acid can be added to theemulsion before the final digestion or after-ripening or it can be addedimmediately prior to the coating.

The silver halide emulsion of a photographic element containing theantifoggants of this invention can contain conventional addenda such asgelatin plasticizers, coating aids, antifoggants such as the azaindinesand hardeners such as aldehyde hardeners, e.g., formaldehyde,mucochloric acid, glutaraldehyde bis(sodium bisulfite), maleicdialdehyde, aziridines, dioxane derivatives and oxypolysaccharides.Sensitizing dyes useful in sensitizing such emulsions are described, forexample, in US. Pats. 2,526,632 of Brooker and White issued Oct. 24,1950, and 2,503,776 of Sprague issued Apr. 11, 1950. Spectralsensitizers which can be used are the cyanines, merocyanines, complex(trinuclear) cyanines, complex (trinuclear) merocyanines, styryls, andhemicyanines. Developing agents can also be incorporated into the silverhalide emulsion if desired or can be contained in a separate underlayer.Various silver salts can be used as the sensitive salt such as silverbromide, silver iodide, silver chloride, or mixed silver halides such assilver chlorobromide or silver bromoiodide.

The silver halide emulsion layer of a photographic element containingthe antifoggants of the invention can contain any of the hydrophilic,water-permeable binding materials suitable for this purpose. Suitablematerials include gelatin, colloidal albumin, polyvinyl compounds,cellulose derivatives, acrylamide polymers, etc. Mixtures of thesebinding agents can also be used. The binding agents for the emulsionlayer of the photographic element can also contain dispersed polymerizedvinyl compounds. Such compounds are disclosed, for example, in US. Pats.3,142,568 of Nottorf issued July 28, 1964; 3,193,386 of White issuedJuly 6, 1965; 3,062,674 of 3 Houck, Smith and Yudelson issued Nov. 6,1962; and 3,220,844 of Houck, Smith and Yudelson issued Nov. 30, 1965;and include the water-insoluble polymers of alkyl acrylates andmethacrylates, acrylic acid, sulfoalkyl acrylates or methacrylates andthe like.

4 halide emulsion layer. Such processes are described in US. Pats.2,352,014 of Rott issued June 20, 1944; 2,543,181 of Land issued Feb.27, 1951; and 3,020,155 of Yackel, Yutzy, Foster and Rasch issued Feb.6, 1962. The emulsions can also be used in diffusion transfer color Thesilver halide emulsion of a photographic element 5 processes whichutilize a diffusion transfer of an imagecontaining the antifoggants ofthe invention can be coated Wise distribution of developer, coupler ordye, from a on a wide variety of supports. Typical supports arecellulight-sensitive layer to a second layer, while the two laylosenitrate film, cellulose ester film, polyvinyl acetal film, ers are inclose proximity to one another. polystyrene film, poly(ethyleneterephthalate) film and While it is preferred to utilize theantifoggants of the related films or resinous materials as well asglass, paper, invention by incorporating them directly into a photometaland the like. Supports such as paper which are graphic element, theantifoggants could also be utilized coated with a-olefin polymers,particularly polymers of by incorporating them into a photographicdeveloper, a-olefins containing two or more carbon atoms, as exemsinceimage formation would still take place in the presplified bypolyethylene, polypropylene, ethylene-butene ence of the antifoggantsand they would still perform their copolymers and the like can also beemployed. antifoggant function.

The speed of the photographic emulsions containing The antifoggingagents of this invention can be inthe antifoggants of the invention canbe further increased corporated to advantage during manufacture insilver by including in the emulsions a variety of hydrophilic colhalideemulsions representing the variations described loids such ascarboxymethyl protein of the type described above. Moreover, fog controlin binderless silver halide in US. Pat. 3,011,890 of Gates, Jr., Millerand Koller films prepared by vapor deposition of silver halide on 21issued Dec. 5, 1961, and polysaccharides of the type desuitable supportcan be achieved by coating the antiscribed in Canadian Pat. 635,206 ofKoller and Russell fogging agents of the invention over the vapordeposited issued J an. 23, 1962. layer of silver halide.

Photographic emulsions containing the antifoggants of 25 The inventioncan be further illustrated by the followthe instant invention can alsocontain speed-increasing ing examples or preferred embodiments thereof;although compounds such as quaternary ammonium compounds, it will beunderstood that these examples are included polyethylene glycols orthioethers. Frequently, useful efmerely for purposes of illustration andare not intended fects can be obtained by adding the aforementionedspeedto limit the scope of the invention. increasing compounds to thephotographic developer solutions instead of, or in addition to, thephotographic emul- EXAMPLE 1 sions. Separate samples of a silverchlorobromide emulsion Photographic elements containing the antifoggantsof containing, respectively, no antifoggant, HgCl and vary the inventioncan be used in various kinds of photoing amounts of RNA are ripened tooptimum sensitivity graphic systems. In addition to being useful inX-ray and and coated on a cellulose acetate film support at a covothernon-optically sensitized systems, they can also be erage of 478milligrams of silver per square foot and 474 used in orthochromatic,panchromatic and infrared sensimilligrams of gelatin per square foot.One set of film tive systems. The sensitizing addenda can be added tocoatings is exposed for 10* second on an intensity scale photographicsystems before or after any sensitizing dyes sensitometer, processed forthree minutes in Kodak D-19 which are used. Developer containing 10milligrams of potassium iodide Silver halide emulsions containing theantifoggants of per liter, fixed, washed and dried. The procedure isrethe invention can be used in color photography, for expeated with asecond set of film coatings except that the ample, emulsions containingcolor-forming couplers or film coating is processed for eight minutes inthe deemulsions to be developed by solutions containing couveloper. Athird set of film coatings exposed three days plers or othercolor-generating materials, emulsions of the 5 earlier and kept at 78 F.is processed for three minutes mixed-packet type such as described inUS. Pat. 2,698,794 in the developer, fixed, washed and dried. Thephotoof Godowsky issued Jan. 4, 1955; in silver dye-bleach graphicresults obtained from these tests are set forth systems; and emulsionsof the mixed-grain type such as in Table I. In this table, D is the lossin density of film described in US. Pat. 2,592,243 of Carroll and Hensoncoatings which have been kept at 7 8 F. for three days issued Apr. 8,1952. after an exposure which produces a fresh density of 1.0;

Silver halide emulsions containing the antifoggants of and D is the lossin density of film coatings which have the invention can be sensitizedusing any of the wellbeen kept at 78 F. for three days after an exposureknown techniques in emulsion making, for example, by which produces afresh density of 2.0.

TABLE I Gone. in 3 minute processing 8 minute "mg/mole processing,Compound Ag Rel. speed Gamma Fog Fog Dr Dz 214 4. 30 0. 22 0. 74 0. 120. 20 180 4. 30 0.08 0. 10 0. 24 0. 44 19s 4. 10 0. 0s 0. 35 0. 12 0. 22190 3. 90 0. 05 0. 24 0.14 0.18 186 3. 76 0. 0s 0. 21 0.06 0. 13 182 3.44 0. 04 0. 20 0. 10 0. 12 17s 3. 44 0. 04 0. 19 0. 05 0. 09

digesting with naturally active gelatin or various sulfur, selenium,tellurium compounds and/or gold compounds. The emulsions can also besensitized with salts of noble metals of Group VIII of the PeriodicTable which have an atomic Weight greater than 100.

The results in the above table show that RNA compares favorably withHgCl in its ability to control extended development fog that it showsless tendency to attack the latent image as evidenced by the resistanceto density loss (D and D for RNA as compared to the mercuric chlo-Silver halide emulsions containing the antifoggants of ride salt.

the invention can be used in diffusion transfer processes which utilizethe undeveloped silver halide in non-image areas of the negative to forma positive by dissolving the undeveloped silver halide and precipitatingit on a silver EXAMPLE 2 This example illustrates the use of RNA as anantifoggant in a high speed silver halide emulsion of the type receivinglayer in close proximity to the original silver used in medical X-rayfilms. Two silver bromoiodide emulsions, one containing no antifoggantand the other containing RNA, are coated on a polyethylene terephthalatefilm support at a coverage of 454 milligrams of silver per square footand 504 milligrams of gelatin per square foot. The coatings are given a5 second simulated blue screen exposure and processed for six minutes inKodak D-l9 Developer containing 10 milligrams of potassium iodide perliter. A second set of coatings, which have been incubated for two weeksat 120 F. and 50 percent relative humidity, are processed in the samemanner. The photographic results obtained from these tests are set forthin Table II.

The results in Table H show that RNA controls incubation fog withoutadversely aifecting sensitometric properties.

EXAMPLE 3 A silver bromoiodide emulsion is prepared corresponding toEmulsion No. 12 described in Empirical Relations Between Sensitometricand Size-Frequency Characteristics in Photographic Emulsion Series byTrivelli and Smith, Photo. Journal, May 1939, page 330. Two samples ofthis emulsion, one (the control) containing no antifoggant and the othercontaining 1.0 gram of RNA per mole of silver, are coated on a celluloseacetate film support at a coverage of 450 milligrams of silver and 1030milligrams of gelatin per square foot. A sample of each film coating isexposed for second on an intensity scale sensitometer, processed forfive minutes in Kodak Developer DK- 50, fixed, washed and dried. Thephotographic results obtained are listed in Table III.

TABLE III Relative Antifoggant speed Gamma Fog The results in Table IIIshow that RNA gives antifoggant action and allow chemical sensitizationto a higher speed.

Although the invention has been described in considerable detail withreference to certain preferred embodiments thereof, it will beunderstood that variations and modifications can be effected Withoutdeparting from the spirit and scope of the invention as describedhereinabove and as defined in the appended claims.

We claim:

1. A composition comprising a photographic silver halide emulsioncontaining a fog-stabilizing amount of ribonucleic acid ordeoxyribonucleic acid.

2. The composition of claim 1 wherein said nucleic acid, ribonucleicacid or deoxyribonucleic acid, is present in an amount of from about0.025 to about 10 grams per mole of silver in said silver halideemulsion.

3. A photographic element comprising a support coated with a silverhalide layer, said element containing a fog-stabilizing amount ofribonucleic acid or deoxyribonucleic acid.

4. The photographic element of claim 3 wherein said layer is a silverhalide emulsion.

5. The photographic element of claim 4 wherein said nucleic acid,ribonucleic acid or deoxyribonucleic acid, is present in an amount offrom about 0.025 to about 10 grams per mole of silver in said silverhalide emulsion.

6. The photographic element of claim 4 wherein said nucleic acid,ribonucleic acid or deoxyribonucleic acid, is present in said silverhalide emulsion.

7. The photographic element of claim 4 wherein said nucleic acid ispresent in a layer contiguous to said silver halide emulsion.

8. The photographic element of claim 7 wherein said ribonucleic acid ordeoxyribonucleic acid is present in said silver halide emulsion.

9. In a process of developing a photographic element comprising asupport coated with at least one silver halide emulsion layer, theimprovement comprising developing said photographic element in thepresence of a stabilizing amount of ribonucleic acid or deoxyribonucleicacid.

10. The composition of claim 1 containing a fogstahilizing amount ofribonucleic acid.

11. The photographic element of claim 3 containing a fog-stabilizingamount of ribonucleic acid.

12. The process of claim 9 in which the improvement comprises developingsaid element in the presence of ribonucleic acid.

US. Cl. X.R. 96-109 Disclaimer 3,512,982.-R0bert U. Taber, William H.Russell, and Charles A. Gofie, Rochester, N.Y. NUCLEIC ACIDS AS FOGSTABILIZERS FOR PHO- TOGRAPHIC EMULSIONS. Patent dated May 19, 1970.Disclaimer filed Apr. 5, 1971, by the assignee, Eastman Kodak Company.Hereby enters this disclaimer to claims 1 through 12, inclusive.

[Ofiimkzl Gazette June 29, 1971.]

